This is part of a study being done by Dr. Salim Azzouz of the McCoy School of Engineering at Midwestern State University. Senior Engineering students were challenged to find and/or design a gearbox that would transform a variable rotational input to an output at a constant angular velocity. This is the resulting study prototype, which uses a printed planetary gear train to accomplish the desired results.If the single shaft is used as the input, it will drive the output (sun gear) at the same speed, however, if a different output speed is desired, the lower shaft on the other side (hub gear) can be driven faster, slower or even counter-rotated to produce the different desired output velocity.This was a close collaboration between the students and myself in design and manufacture. Extensive work was done in SolidWorks, resulting in a functional digital assembly. The gears and carrier plate were printed on our Makerbot, the axles turned from aluminum stock on a CNC lathe and the support structure cut from Makrolon, an impact resistant, clear plastic. Delrin bearings were purchased from mcmaster.com.Further study is planned, connecting the input and differential to motors, monitoring the velocities of each of the shafts with tachometers, recording the results at varying speeds and comparing the observed results with the theoretical calculations.